1. Technical Field
The present invention relates to an electrophoretic display device, an electronic apparatus, and a method of driving an electrophoretic display device.
2. Related Art
An electrophoretic display device is formed so that electrophoretic fluid dispersion that includes one or more types of electrophoretic particles and an electrophoretic dispersion medium is sealed between a pair of opposite electrode plates, at least one of which is transparent. Applying a voltage between the two electrodes causes electrophoretic particles to move in the electrophoretic dispersion medium, and a change in dispersion of the electrophoretic particles varies optical reflection property to thereby make it possible to display information. At this time, if one of the electrodes is formed of a plurality of divided pixel electrodes, by controlling an electric potential of each pixel electrode, a difference in dispersion of particles in each pixel is produced to thereby make it possible to form an image.
Each pixel electrode is connected to a TFT (Thin Film Transistor), which is a switching element. By applying a predetermined voltage to the gate electrode of the TFT, the TFT enters an on state to cause a drain current to flow, so that the connected pixel electrode is supplied with an image signal. Note that it has been suggested that the TFT may employ a flexible, light organic transistor that allows cost reduction.
JP-A-2002-149115 describes an active matrix electrophoretic display device that uses electronic ink. The electrophoretic display device described in JP-A-2002-149115 employs a driving method in which, when a display content is changed, all the pixel electrodes are set to the same electric potential and a voltage is applied between the common electrode and the pixel electrodes to thereby erase the content displayed at that time over the entire display area, and, after that, another display content is displayed.
When a TFT is made to enter an on state, for example, a P-type transistor is applied with a negative voltage and an N-type transistor is applied with a positive voltage; however, in terms of transistor structure, it has been known that, if the gate electrode of a P-type transistor is applied with a negative bias voltage or the gate electrode of an N-type transistor is applied with a positive bias voltage, carriers are trapped on a semiconductor surface. Trapping of carriers leads to fluctuation in threshold voltage at a boundary between an on state and an off state of a transistor or fluctuation in drain current in an on state of the transistor. This results in a decrease in contrast of the electrophoretic display device or may produce a problem such as nonoperation of the electrophoretic display device in some cases. Particularly, the organic transistor noticeably has a problem of characteristic degradation due to the carrier trap. The above problem regarding fluctuation in threshold in an organic transistor is also described in “Bias-induced threshold voltages shifts in thin-film organic transistors” H. L. Gomes, P. Stallinga, et. al., APPLIED PHYSICS LETTERS, Vol. 84, No. 16, 19 APR. 2004, p 3184-p 3186 and “Light-induced bias stress reversal in polyfluorene thin-film transistors” A. Salleo, R. A. Street, JOURNAL OF APPLIED PHYSICS, Vol. 94, No. 1, 1 JUL. 2003, p 471-p 479.